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27 TABLE 3-5 Summary and description of reference site data used in the analysis Road type State Description Miles Mile- All crashes Fatal and Average years injury AADT crashes Two-lane Pennsylvania Untreated two-lane 170 1690 2332 455 4517 roadways roadway sections New York Untreated two-lane 182 1683 2400 1211 4300 roadway sections New Jersey Before-period data of 191 1337 8737 3338 12737 treatment sites Illinois Before-period data of 460 2755 2783 706 22850 treatment sites Four-lane Missouri Before-period data of 1826 14801 30274 9642 13560 freeways treatment sites Pennsylvania Before-period data of 779 3807 5750 741 24995 treatment sites New York Untreated two-lane 122 1098 3387 1497 12870 roadway sections Wisconsin Before-period data of 456 2280 10831 2714 20900 treatment sites Four-lane Pennsylvania Before-period data of 106 503 725 126 13810 divided treatment sites expressways Wisconsin Before-period data of 145 725 2174 361 11770 treatment sites PRPMs. This meant that data availability for the purpose of TABLE 3-6 Crash data variables obtained from each state calibrating the SPFs would be nonexistent for the period after Category Variable nonselective installations were implemented and could be Time variables Crash date scarce toward the completion of the nonselective installa- Crash time tions statewide. To calibrate the SPFs for these later years, a Environmental variables Road surface condition comparison group of sites was identified that consisted of as- yet untreated locations or locations on which PRPMs had Weather condition been installed prior to the beginning of the study period. The Light condition comparison group accounted for time trends throughout the Crash-related variables Impact type SPF calibration period. Special attention was given by the Crash severity research team when selecting roadways to avoid any road- Initial direction ways near PRPM locations in order to minimize the influence Vehicle maneuver of any spillover or migration effects. Alignment Because of the widespread implementation of PRPMs in Location type (intersection vs. nonintersection) Illinois, it was not possible to select a suitable comparison Roadway variables Route number group of sites in this state. Thus, for this state, SPFs were fit- ted to the data for the later years of the after period to develop Milepost or reference point and offset time trend factors for these later years. However, in Wisconsin, the widespread implementation of TABLE 3-7 Crash data period, source, PRPMs on four-lane freeways and expressways during 1999 and roadway referencing system resulted in very limited comparison group data for a total of State Period Source Referencing System 43 miles of four-lane freeway. To address this constraint and to Illinois 19912000 Highway Safety County, route, milepoint account for time trends in more recent years (i.e., 19982000), Information System the research team collected additional data for urban Interstate (HSIS) highways in Madison County, Wisconsin. Missouri 19912000 Missouri DOT Route, milepoint New Jersey 19911998 Internet/New Jersey Route, milepoint (excluding DOT 1996) 3.2.3 Crash Data New York 19912000 New York DOT Reference marker Pennsylvania 19912001 Pennsylvania DOT County, route, segment, offset The crash databases obtained from each state contained the variables listed in Table 3-6. Table 3-7 shows the period Wisconsin 19942001 Wisconsin DOT Route, reference point, offset